Not too sad to do in situ but really depends what you used to seal the sump in the first place? If you've used silicon sealer then really you should remove the sump entirely, clean it up and then refit etc - this would involve jacking the engine up as high as poss off it's mounts and dropping the front ARB down, to enable enough clearance to get the sump out and clear. You'll need to drop the oil pickup off as well, as that gets in the way.
but if you've used a rubber gasket - you can drop the sump down sufficiently in situ to use a bit of sealant on it and then reseal.
Either way, you'll need to remove the bolts for the plenum to block to gearbox supporting bracket so that you can get to the last sump bolt in the far back corner drivers side.
as standard they dont have a gasket nissan used instant gasket.
silicone sealent is a bit bodge it and scarper(not being keyboard warrior it really is) get a tube of proper instant gasket and put quite a lot on it then glue it in place so to speak. it may prove easier just to whip engine out engine as it only takes a couple of hours(our record is two and a half but ppl like sideways danny have done it in silly quick times )